Stereo-cameras exist, which are able to derive three dimensional (3D) information of an object.
In state of the art stereo-camera systems, the distance between the multiple cameras is fixed.
As objects can though be moving around in the captured scene, the depth of the object can often not be measured with optimal precision.
Moreover the state of the art methods and systems require excessive amount of cameras in their stereo-camera set-up and a lot of processing power.